Is brain tetrahydrobiopterin (BH4) associated with protein synthesis in addition to serving as the required cofactor for tryptophan and tyrosine hydroxylases (TPOH and TOH)? Regional distributions of BH4 across subcellular fractions of monoamine-specific cell body and nerve terminal regions do not correlate with demonstrated distributions of TPOH and TOH activities. The following questions will provide the foci for our experimental goals: 1) Do BH4 levels codistribute in subcellular fractions with monoamine products or limiting substrate levels? 2) Does the stimulant drug d-amphetamine which uniquely reduces total striatal levels of BH4 do so as a result of its inhibition of protein synthesis in the S2 fraction? Will this drug, which reduces fractional TPOH and TOH activities (associated with BH4 or protein synthesis decreases, or both?), also effect a selective loss of BH4 in the soluble (S2) fraction? 3) Do the longer acting halogenated derivatives of amphetamine, which like d-amphetamine disaggregate polysomes and reduce TPOH activity levels in striatal subcellular fractions, also reduce BH4 levels in the soluble (S2) fraction? 4) Do "similar" stimulant drugs, cocaine and methylphenidate which do not reduce striatal BH4 or TPOH activity levels effect the subcellular distribution of BH4 or the level of protein synthesis in the soluble fractions of monoamine-specific regions? 5) Does the non-pharmacologically induced BH4 decrease that occurs diurnally take place selectively in the same fraction as the amphetamine-induced one, and also as a possible correlate of soluble protein synthesis inhibition? 6) Do changes in BH4 concentrations of any of the above paradigms effect the activity level or the stability of TPOH activity? The following techniques will be applied to regional subcellular fractions of rat brain. High performance liquid chromatography (HPLC), reverse-phase techniques will be used to measure endogenous BH4 levels; HPLC and radiometric techniques for TPOH activity 3H lysine incorporation for in vivo protein synthesis; and isoelectric focusing (IEF) and thermal inactivation techniques to characterize enzyme stability. Deficiencies of BH4 in man are associated with severe pathologies such as dystonia, depression, Alzheimers's, Parkinson's. The biosynthesis of neurotransmitters requiring BH4 may be epiphenominal to protein synthesis in some cases of BH4-deficient pathologies including those associated with some stimulant drug abuses.